Here is my ceramic double track tunnel portal after some touch up painting and adding some lichen, which I did this evening:
I think it's better, but looks a little contrived. It looks like I added the lichen to hide the seams, which is, indeed, the case. I will let it rest and revisit it in a day or two.
For my next project, I have another pair of ceramic single track portals. They will be used to replace the plastic red brick portal shown in the photo below:
Arnold